The present invention pertains to an apparatus and a method for packaging, mixing and delivering bone cement. More particularly, the present invention relates to apparatus for intimately mixing at least two components of bone cement wherein the components are initially kept in separate compartments of a flexible package.
The natural joints of the human body often undergo degenerative changes due to various etiologies. When these degenerative changes are advanced, irreversible and unresponsive to non-operative management, it may ultimately become necessary to replace the natural joint with a prosthetic device. When such replacement becomes necessary, the prosthetic device which is implanted is often secured to the natural bone by using bone cement.
Bone cement that is used to secure prosthetic devices to bone is comprised of a liquid monomer component that polymerizes about a polymeric powder component. In this regard, bone cement is generally formed from a methyl methacrylate monomer and poly (methyl methacrylate) or methyl methacrylatestyrene homo- or copolymer. The polymeric powder component of bone cement usually comprises particles composed of spherical beads that may be obtained by a suspension polymerization process. The beads are generally sieved to comply with particular size specifications. The powder component may also comprise particles that have been milled or crushed.
The preparation of bone cement generally involves mixing the polymer and monomer components in a suitable reaction vessel to form the bone cement. Generally, it is necessary that the components of bone cement be uniformly and thoroughly mixed so that a homogenous product is obtained. Increased homogeneity of the blend and minimal porosity are particularly desirable in providing a cement mixture that is easy to work with, yet maintains satisfactory mechanical properties. In producing bone cement it is crucial to maintain the liquid and the powder components separate until just prior to use and to avoid exposure of the components to the atmosphere because of the potentially malodorous nature of volatilized components of the bone cement.
There have been several approaches heretofore pertaining to the packaging and admixing in situ of a plurality of reactive components, also for cement products wherein the temporarily separated particulate solid component and liquid component are first combined, and then admixed in the packaging, without exposure to the atmosphere just prior to use. Representative approaches are disclosed in U.S. Pat. Nos. 2,874,830; 3,082,867; 4,041,214; 4,973,168; 4,463,875; and 5,114,240; and in PCT WO 86/06618.
The packaging systems proposed heretofore for use in the manufacture of bone cement products have often been found to have serious disadvantages when tested for commercialization. Quite often the packaging is overly complicated and expensive.
Some suggestions include the incorporation of diverse mechanical mixing devices into the packages in effort to attain the desired homogeneity and reduced porosity. Such devices are not only cumbersome, but the results obtained from using such devices are dependent on the skill and care of the individual performing the mixing operation. In this regard, the quality of the resulting bone cement in terms of porosity and homogeneity depends on the accuracy of transfer of the components, the mixing time, the mixing pattern and mixing speed, and if vacuum is used, on the time and pressure as well as the degree of mixing occurring under vacuum. All of the aforementioned parameters are determined by the individual operator and, as a result thereof, the homogeneity and the extent of polymerization (i.e., rheology of the cement during application) are neither consistent nor readily reproducible.
Accordingly, a need exists for a simple and inexpensive bone cement packaging system which will allow mixing of two or more components while avoiding the above-mentioned disadvantages.